Four GPU's versus two GPU's
"Better" is not the question... it is the wrong word to use, as it depends.

4 GPUs will render 4 tiles simultaneously so rendering an image will be faster than with 2.

Memory: GPUs cannot share vRAM, once you hit the limit the GPU will fail.

So it all depends on the complexity of the scene you are trying to render, or how long can you wait for the render to be done.